Classification and etiology of strictures

A ureteral stricture is a pathologic narrowing of the ureter, resulting in dilation of the urinary system proximal to that point with resultant delayed urine transit. Strictures may be extrinsic, intrinsic, or intraluminal. This classification system is valuable since the different types of obstruction may be treated differently. For example, intraluminal obstruction may be successfully treated by endoscopic ablation or removal of the obstructing agent, while extrinsic obstruction is difficult to treat endoscopically and requires drainage and treatment of the extrinsic etiology of the obstruction.

Strictures can also be classified as ischemic or non‐ischemic. This definition is also clinically relevant because ischemic strictures may not respond as well to endoscopic procedures [8]. Strictures have also been classified as inflammatory versus non‐inflammatory [9], but it is unclear if there is any clinical relevance to this classification system [10]. Table 52.1 lists the etiologies and classifications of ureteral obstruction.

Strictures often arise iatrogenically due to surgery, by clipping, suture ligation, thermal injury, or devascularization. Gynecological surgery is the most common cause of iatrogenic ureteral injury and hysterectomy is the leading procedural cause, occurring at a rate of 0.5–1.5% [10, 11]. Abdominal hysterectomy is more likely to lead to ureteral injury (2.2%) compared to vaginal hysterectomy (0.03%) [10]. Unfortunately only 13–66% of injuries are detected intraoperatively, with the remainder diagnosed postoperatively [10].

The incidence of ureteral injury from colon and rectum surgery is on the rise [4, 12]. The types of colorectal surgery most likely to injure the ureter are transverse colectomy (0.05%), right hemicolectomy (0.08%), proctocolectomy (0.26%), left hemicolectomy (0.28%), sigmoidectomy (0.33%), subtotal/total colectomy (0.35%), anterior resection (0.58%), and abdominoperineal resection (0.76%) [12]. Rectal cancer is the most common underlying disease associated with ureter injury at the time of colorectal surgery [12].

Urological surgery is another well‐recognized cause of ureteral stricture. In the initial experience of endoscopic stone treatment, large‐caliber ureteroscopes [13] and lithotrites like the electrohydraulic probe led to a major complication rate (defined as perforation, avulsion, or stricture) of 6.6% [14]. In the modern era, with the advancement of technology to include smaller, tapered, and more flexible ureteroscopes and instruments the stricture rate for uncomplicated ureteroscopy is 0.3–0.6% while the perforation rate for intact extraction of stones is 4% [15, 16]. The danger arises when these injuries are not recognized intraoperatively, and are associated with silent obstruction, risking renal loss. This concern has led the American Urological Association to recommend routine ultrasound of upper tracts following ureteroscopic manipulation for stone removal [17].

A long‐standing, impacted, ureteral stone can also lead to ureteral wall damage and stricture formation (Figure 52.2). Roberts et al. reviewed 21 patients with long‐standing ureteral stones (mean 8 months) [18]. After treatment, 24% developed strictures. The authors identified longer duration of impaction and iatrogenic ureteral perforation during ureteroscopy as risk factors for future stricture formation [18].

An entity called congenital mid‐ureteral stricture represents a rare cause of mid‐ureteral obstruction and may be confused with either ureteropelvic junction or ureterovesical junction obstruction. This highlights the importance of retrograde pyelography prior to treatment of ureteral strictures [19, 20]. Segmental excision is curative and the etiology may be chronic in utero ischemia at the level of the mid ureter because of the vascular watershed between the aorta and iliac vessels.

Presentation

An injury to the mid ureter may present clinically in a variety of ways. In the case of acute iatrogenic ureteral transection the patient may be acutely septic while in the case of a ligated but intact ureter, the patient may present with ipsilateral flank pain, recurrent pyelonephritis, and/or an unexplained rise in serum creatinine. Urine extravasating into the peritoneal cavity may cause peritoneal irritation and findings of an acute abdomen. In contrast an incomplete stricture may be asymptomatic, and identified incidentally only upon abdominal imaging. In an international review of almost 2000 ureteroscopy patients, the majority of strictures were symptomatic but three (0.15%) were asymptomatic. The presence of pain after stent removal had a 64.3% positive predictive value and a 99.8% negative predictive value for stricture.

Diagnosis

There are several methods available to assist the urologist in the evaluation of strictures (Table 52.2). One of the simplest and least invasive initial studies is ultrasonography. B‐mode ultrasound will detect dilation of the renal pelvis and/or calyces although ureteral dilation is sometimes obscured by overlying structures or bowel gas. Using Doppler sonography the resistive index (RI), defined as [peak systolic velocity − end diastolic velocity]/peak systolic velocity, is generally less than 0.7 in an unobstructed system [21]. Although a RI above 0.75 is correlated with obstruction, compared to normal kidneys (RI 0.6) and healthy controls (0.58; P < 0.05) [22], a threshold RI of 0.7 has only a 44% sensitivity and 82% specificity for diagnosis of ureteral obstruction [23].

Historically intravenous pyelography was employed in the diagnosis of suspected ureteral injuries (Figure 52.3). This modality is still available in many centers, although the results are not as sensitive or as specific as computed tomographic (CT) urography [24].

CT imaging represents the most common modality employed to evaluate ureteral obstruction. Unenhanced CT scanning is the gold standard for the initial evaluation of suspected nephrolithiasis [17], but does not reliably determine non‐stone‐related causes of ureteral obstruction. In such instances, CT urography provides superior spatial and contrast resolution by opacification of the collecting system [25] enabling it to detect stones, urothelial masses, and congenital anomalies. Disadvantages of CT urography include the need for intravenous contrast, which can lead to nephropathy (defined as a rise in serum creatinine of 0.5 mg/dl or 25%) and contrast allergy [26]. Risk factors for contrast nephropathy include renal impairment, diabetes, age, congestive heart failure, dehydration, multiple myeloma, and high‐osmolality agents [26], and these risk may be mitigated by hydration, discontinuation of nephrotoxic agents, reduced contrast dose, N‐acetylcysteine, and use of iso‐osmolar or low‐osmolality contrast medium. When precise anatomical details are required and intravenous contrast is contraindicated, CT pyelography can be performed by injecting contrast through a nephrostomy, or by direct needle puncture of the collecting system. In a study by Ghersin et al., CT pyelography successfully detected the cause of ureteral obstruction in 20/20 patients who failed first‐line imaging [25].

Diuretic renography provides objective evidence regarding ureteral obstruction. In this procedure the patient is hydrated and challenged with furosemide (usually 40 mg intravenously), administered when the tracer peaks in the affected system. Obstruction is defined as the time required to clear half of the radionuclide (T½) greater than 20 minutes, while a T½ of <10 minutes is considered unobstructed. T½ times between 10 and 20 minutes are indeterminate [27]. However, if furosemide is given too early during the filling phase it may lead to a flat drainage curve and a false impression of poor drainage [28]. In addition, severe hydronephrosis and chronic renal insufficiency may lead to false positive results [28, 29]. It is also important to remember to place a bladder catheter in patients with vesicoureteral reflux, high bladder storage pressures, or those with indwelling ureteral catheters [28].

Magnetic resonance (MR) urography is also useful for identifying ureteral obstruction. Semins et al. compared MR urography in a 3‐T scanner with HASTE sequences to noncontrast CT in colic patients [30]. MR had an 84% sensitivity for obstruction but identified a stone in only 50% of patients with stones on CT [30]. Specific situations where MR urography may be useful are in radiation‐sensitive populations such as children, pregnant women (done without gadolinium), and patients with extensive prior radiation exposure. In an iatrogenically created ureter obstruction animal model the sensitivity and specificity of diuretic renal scintigraphy, MR urography, and ultrasound RI were 93.3 and 88.8%, 86.6 and 77.5%, and 86.6 and 77.5% respectively. However, no one modality was able to correctly predict all cases of obstruction‐related apoptosis [31].

Antegrade and retrograde pyelography are familiar to most urologists, simple to perform, and the results are usually easy to interpret (see Figure 52.4). However, these techniques require radiation exposure and are invasive, usually requiring an anesthetic. These modalities provide the stricture severity, length, and potential etiology.

The invasive Whitaker test assesses whether hydronephrosis is obstructive by antegrade perfusion of the kidney with saline or dilute contrast at 10 ml/min. The pressure is measured simultaneously within the renal pelvis and bladder. Obstruction is diagnosed when the renal pelvis minus the bladder pressure is >22 cmH₂O [32]. This test may underdiagnose obstruction in the face of massive hydronephrosis [33]. Usually, the Whitaker test is performed when there is disagreement between other imaging modalities leading to ambiguity in the diagnosis [32].

Intraluminal ultrasound using a 12.5–30.0 MHz probe deployed in the ureter may provide information regarding the nature of the ureteral wall and periureteral tissues, and information regarding any associated foreign body (stone) within the ureter or periureteral tissues [34]

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